Transmission measuring system



June 3, 1941. J. F. ANDREWS TRANSMISSION MEASURING SYSTEM Filed Sept.26, 1939 Sad MSSQ y# SS@ m @@aws ATTORNEY INVENTOR JEM-awww@ .gummwReissued June 3, 1941 UNHTED STTS ATENT FFICE.

TRANSMISSION MEASURING SYSTEM Application September 26, 1939, Serial No.296,687

llZ Claims.

This invention relates to transmission measuring systems andparticularly to a method and means whereby the transmission efficiencyof a signaling circuit may be measured in both directions by a testmanat one end of the circuit, the necessary connections at the far endbeing automatically made by the said testman.

Heretofore, it has been customary to test each signaling circuit, suchas a toll or long distance circuit, at stated intervals of timedepending upon the type of circuit, the number of tests ranging from twoper week to two each year. Since each measurement requires from five totwelve minutes at each circuit terminal, and, in addition involves notonly the services of the testman but also the assistance of twooperators to make the circuit connections at those terminals, it isobvious that a large amount of time and labor are expended to completethe measurements in those oices where a large number of circuitsterminate.

One o the objects of the present invention is to simplify the procedurerequired for the making of such transmission test and thereby to reducethe amount of time necessary for the making of such test.

Another object of the invention is to enable the testman toautomatically select the circuits to be tested and to make the necessaryconnections at both ends of the selected circuit for the4 making of atwo-way transmission test upon the selected circuit.

The manner in which those and other objects of this invention areattained will be apparent from the following description when read inconnection with the attached drawing that shows schematically one formof embodiment of the invention.

In the drawing L1 and L2 represent two toll or long distance circuits,hereinafter referred to as signaling circuits, that extend from office Ato oiiice B. Such circuits would have at each terminal thereof the usualterminal apparatus, butfor the purpose of simplicity such apparatus isomitted from the drawing since it forms no part of the invention. Atofce A the circuit L1 is connected by the conductors 66 and 6| to thecontacts I and I', which contacts form part of the upper bank ofcontacts of the selector shown at the right-hand side of the ligure.Contact I is connected to Contact 2, and likewise contact I is connectedto contact 2', the purpose of which will be later made clear. In likemanner the circuit L2 is connected by conductors 62 and 63 ,to contacts3 and 3 of the same bank of contacts,

which contacts are connected to contacts 4 and Il', respectively. Inlike manner other signaling circuits, similar to L1 and L2, may beconnected to other pairs of contacts in the upper bank of the selector.The wiper contacts and 5|, which are supported by the shaft 52, areadapted to be moved by steps across the contacts, I, I', 2, 2 etc.whenever the shaft is rotated. The wiper contacts 50, 5I are connectedto the wiper contacts 53, 5ft, respectively, which are adapted to bemoved by steps across the contacts II, lIl', I2, I2', etc. that formpart of the middle bank of contacts of the selector.A The odd numberedcon.. tacts of that bank are connected together, and likewise the oddnumbered primed contacts are connected together and all contacts thusconnected are in turn connected to the generator 55. That generator isrepresented as producing 1,000 cycle current at a xed output of onemilliwatt, but, of course, other values of frequency and of power mightbe employed. The even numbered contacts of the middle bank and also theeven numbered primed contacts of that bank are connected together, andare in turn connected to the even numbered contacts (primed andunprimed) in the lowest bank of the selector. The wiper contacts 56, 51which are adapted to move by steps across the contacts of the lowestbank are connected to the measuring device 58. All of the odd numberedcontacts of the lowest bank are connected together and likewise all ofthe odd numbered primed, and those contacts, thus connected, are in turnconnected to the circuit L3 that extends between ofice A and office B.The resistance networkV 59, which is shown between La and the selector,furnishes the means for adjusting the deflection of the needle of themeter 58. This adjustment is necessary to compensate for variations inthe net loss over the tone circuit L3. The network should be adjusted toaiford the proper deflection of the needle upon the scale of the meter.This adjustment should be made prior to transmitting current in eitherdirection over circuits such as L1 and L2. With the generator 'I3transmitting current of a denite frequency and magnitude over thecircuit L3, the deflection of the needle would be properly positione'd,say at zero, by suitable adjustment of the network 59.

The shaft 52 of the selector at oice A is adapted to be rotated by meansof the arrangement shown at the bottom thereof. This comprises a ratchetcylinder 64 which is attached to the shaft and may be rotated one stepat a time, by the operation of the magnet 65, That magnet winding isconnected in series with the battery 66 and the winding of the relay S?.A dial key 8| serves to operate the device.

The selector may be of the type shown in Fig. 380 upon page 516 ofTelephony by MclVIeen and Miller (1912 edition). As there shown thedevice is arranged also to elevate the shaft vertically so that each setof wiper contacts might cover more Vthan one bank of fixed contacts, butfor the sake of simplicity such elevating mechanism has been omittedfrom the applicants drawing.

At the distant oince B another similar selector is employed. Theadjacent contacts Si and 32 of the upper bank are connected together,and similarly connected are the contacts Si and 32. Each pair thusconnected is in turn connected to one of the circuits L1 and Le; and asshown on the drawing, other pairs of connected contacts of that bank maybe connected to other signaling circuits. The Wiper arms 68, 6g thatmove across the upper bank of contacts are connected to the wiper armsit?, 'Il respectively, that move across the contacts of the lower bankof the selector. rThe odd numbered contacts of the lower bank areconnected together, and the odd numbered primed contacts likewise areconnected together. And those contacts are connected to the input sideof the amplifier 12. The even numbered contacts of that bank, andlikewise the even numbered primed are connected to the generator E3which, for theV purpose of illustration; is indicated as producing onemilliwatt of power at 1,009 cycles. The generator is also connected tothe circuit L3, and at the point oi its connection to the circuit In, animpedance is shunted thereacross. That impedance is represented by theconden'sers 'it and 'l5 and an element l 'whose resistance varies withthe amount of current passing therethrough. The element maybe a boron oruranium oxide bead, and, as shown in the drawing, the element isconnected in the output circuit of the amplifier 'l2 in series with therec'tier l?, `so that its resistance is re-V sponsive to the outputcurrent of the amplifier. The selector at voice B is stepped around bythe magnet i3 which is connected to the back contact of the relay i9.The winding of the latter relay is connected to the circuit In, which,for example, may be a telegraph circuit extending between office A andoice T:l.

The manner in which the transmission ef ciency or" the line L1 isdetermined is as follows: The testman at cce A operates the dial key 8lwhich `energizes the magnet 65 suiiiciently to attract its armature andthereby to effect the rotation of the shaft 52 one step. VThat bringsall of the wiper contacts upon the first xed contacts of theirrespective banks. Furthermore; by the operation of the dial key 8l relay61 becomes deenergized, and, upon the release of its armature, relay i9at the distant oiiice is energized. That removes the battery from themagnet 'F8 and results in the rotation of the shaft Bti one step,thereby bringing the wiper contacts of that selector into engagementwith the iirst contacts of their respective banks. With the circuit thusarranged current'will flow from the generator 55 over a circuit thatincludes the odd numbered contacts oi the middle bank of contacts, arms53 and 5S, contact l, the upper conductor of circuit L1, contact 2li 0fthe upper bank at olice B, arms 6B and i9, the odd numbered contacts ofthe lower bank to one terminal of the input side of amplifier 72, thencefrom the other terminal of the input side to contact fil, wiper contacts'H and 69, contact i', the lower conductor or" circuit L1, conductoriii, contact I', wiper contacts 5i and 5s and the odd numbered primedcontacts of the middle bank of contacts at oiice A to the other side ofthe generator 55. Simultaneous with the transmission of the current overthe line L1 current will be transmitted from generator 'i3 at oice Bover the circuit Le to the measuring device '58 which is connected tothe wiper contacts 56 and 5l, Whichrest upon the contacts 2l and El ofthe lowest bank or" contacts of that selector. The output of thegenerator 'i3 is shunted by the impedance la, 15, i6. As long as thatimpedance remains fixed the magnitude of the current transmitted overthe line L3 from 13 will likewise remain xed. However, as pointed outhereinbeiore, the magnitude of the impedance l, l5, l5 is susceptible ofvariation due to the effect of the rectified current impressed thereonby the amplifier 712-, which current'de'- ponds, in magnitude, upon theamount of current received from the circuit In. risv the element 'itvaries in resistance due to changes in the amount of current received atoiiice -B4 over the circuit L1, the amount of current sent over thecircuit In from the generator 'F3 will Vary from normal and suchvariation will be shown upon the measuring device et. Those variationsare a measure of the transmission eiiiciency of the circuit Li whentransmitting in the direction from oice A to ofce B;

Upon the completion of the mak-ing of that measurement the circuit isthen arranged to measure the transmission efficiency in the oppositedirection, i. e. from Yoiiice B to oirc'e A. This is accomplished byanother operation of the key Si by the testman at office That operationcauses the wiper contacts 'of the selectors at oiice A and oice B tomoveone step in the direction of rotation. The eiect of that at office A isto disconnect generator 55 from the circuit L1 and to connect theretothe meas'- uring device thereby making possible the measurement ofcurrent transmitted from the distant end of L2. The connection isestablished in the following manner. When the wiper contacts' and 5Irest upon the "contacts 2 and 2', the circuit L1 will be connected tothe wiper contacts 53, 54 which rest upon contacts l2 and i2. The evennumbered contacts of the middle bank are connected tothe even numberedcontacts of the lowest bank of that selector.V Since th'e wiper contacts55' and 5? are at that instant resting upon cont-acts 22 and 22 of thelowest bank, the measuring .device 58 will, therefore, be connected tothe circuit L1.

At the distant oiiice B the wiper contacts are likewise upon the secondcontacts of each bank of contacts. Accordingly the dista-nt end ofci-r`A` cuit L1 which is connected to the xed contacts '$2 and 32 willbe connected therethrough Vto the wiper contacts t8 and 69, which are inturn connected to the wiper contacts 'iii and il which rest upon xedcontacts 62 Vand G2. The flatter contacts are connected to the outputside of generator 'i3 so that current from that generator will betransmitted over the circuit just traced to the terminal of the circuitL1 at 'office B; The current or power transmitted `overcircuit L1 willbe measured by the device 53, and such reading is 'a measurement Aof theemciency of thatI circuit intransmitting inthe direction from office Bto oice A'. If the testing of other circuits is unnecu essary orundesired a clearing out signal may be sent by means of the dial key 8lto disconnect the measuring apparatus by rapidly stepping around theselector switches at the several ofces. If, however, it is desired totest other circuits, the procedure is as follows:

Upon the completion of the making ofthe twoway measurements of thetransmission efficiency of the circuit L1 in the manner above describedthe testman again operates the key 8|. That causes the selectors atoffice A and ofiice B to move another step in the direction of rotationwhich brings the wiper contacts upon the third contacts on each bank ofthe several selectors. That serves to connect generator 55 at office Ato the circuit Lz for the purpose of measuring the transmissionefficiency of that circuit in the direction from office A to oice B.Upon the completion of the making of that measurement the key 8i isagain operated, which causes both selectors to move another stepforward, and the apparatus is then connected to measure the transmissioneciency of the circuit L2 in the direction from ofiice B to oice A.

By means of the system hereinbeiore described transmission measurementsin both directions upon a given circuit may be quickly made by a onetestman operating at one end of the circuit. Such system not onlygreatly reduces the amount of time heretofore required in the making ofsuch test, but also reduces greatly the amount of labor required andthereby reduces the cost of making such tests.

While this invention has been disclosed as embodied in a particularform, it is capable of embodiment in other and different forms withoutdeparting from the spirit and scope of the appended claims.

What is claimed is:

l. In a transmission measuring system the come bination with a signalingcircuit, whose transmission eiciency is to be measured between twoterminals thereof, of a source of current of xed magnitude connected tothe near end of said circuit, a second circuit coterminous with the saidrst mentioned circuit and having a source of current of fixed magnitudeconnected thereto at its distant end and a current measuring instrumentconnected thereto at its near end, a shunt connected across said secondcircuit at its distant end and means responsive to the current in thesaid rst mentioned circuit to vary the conductivity of the said shuntwhereby the magnitude of the current iowing through the said secondcircuit is proportional to and a measure of the transmission eiiiciencyof the said first mentioned circuit.

2. In a transmission measuring system, the combination with a signalingcircuit, whose transmission eiiiciency is to be measured, of a source ofcurrent of fixed magnitude, switching means to connect said source tothe near end of said circuit, an amplifier, a second switching means toconnect the far end of said circuit to the said amplifier, a secondcircuit coterminous with the said iirst mentioned circuit and having asource of current of fixed magnitude connected across the far endthereof. a shunt connected also across the far end of the said secondcircuit, the said shunt being connected to the output of the saidamplier, and including an impedance whose conductivity varies with thestrength of the output current of the said amplifer, a current measuringdevice and switching means to connect the said measuring device to thenear end of either the said second circuit or the said signalingcircuit.

3. In a transmission measuring system, the combination with a signalingcircuit, the transmission eiciency of which is to be measured, of asource of current adapted to be connected to the said signaling circuit,a second circuit coterminous with the said signaling circuit, a secondsource of current connected to the distant end of the said secondcircuit, a device for measuring the current transmitted over the saidsecond circuit, and means controlled by the current transmitted over thesaid signaling circuit to vary the magnitude of the current transmittedover the said second circuit.

4. In la transmission measuring system, the combination with a signalingcircuit, the transmission efilciency of which is to be measured, of asource of current to be transmitted over the said signaling circuit,switching means to connect the said source to the said signalingcircuit, a second circuit coterminous with the said signaling circuit, asecond source of current connected to the said second circuit fortransmission thereover, `a current measuringl device adapted to beconnected to the said second circuit, and a controllable impedanceadapted to be connected across the output of the said second source ofcurrent and responsive to the current being transmitted over the saidsignaling circuit to render the magnitude of the current beingtransmitted over the said second circuit proportional to the magnitudeof the received current in the said signaling circuit.

5. In a transmission measuring system, the combination with a signalingcircuit, the transmission eiciency of which is to be measured of asecond circuit. coterminous with the said signaling circuit, a source ofcurrent of xed magnitude for connection with the said signaling circuitat the near end, a current meter for connection with each circuitalternately, switching means controllable at will to simultaneouslyconnect said source of current ,to said signaling circuit and said meterto said second circuit, or to disconnec-t saidY meter from the saidsecond circuit and connect said meter to said signaling circuit wheneversaid source of current is disconnected therefrom, and a second source ofcurrent connected to the distant end of said second circuit but adaptedalso for connection to the distant end of the said signaling circuit, acontrollable impedance connected across the distant end o1 said secondcircuit and arranged to shunt a portion of the current from the saidsecond source and a second switching means at the far end to alternatelyconnect the signaling circuit to the said controllable impedance or toconnect the said second source of current to the far end of saidsignaling circuit.

6. The method of measuring the transmission eiiiciency of 'a signalingcircuit which consists in applying to that circuit a xed amount ofpower, simultaneously applying power to the distant end of a secondcircuit, coterminous with the said first circuit and measuring theamount of power received at the near end of said second circuit, andcontrolling the amount of power applied to the distant end of the saidsecond circuit by and in accordance with the amount of power received atthe distant end of the said signaling circuit.

7. The method of measuring the transmission emciency of a signalingcircuit which consists in applying a known amount of power to the nearend of the signaling circuit and controlling by the'amount of powerreceived 'at the distant end of that circuit the amount of power thatmay be transmitted over another circuit from the distant end` thereof,the said other circuit being cotermlinous with the said signalingcircuit, and measuring the amount of current received at the near end ofsaid other circuit.

8. The method of measuring the transmission efficiency of a signalingcircuit, which consists in applying a known amount of power to the nearend of the signaling circuit, rectifying the current/received at the farend of the said signaling circuit and utilizing that rectified currentVto control the magnitude of the current transmitted from the distantend of a second circuit, cotermincus with the said signaling circuit,and measuring the amount of current received at the near end of the saidsecond circuit.

9.` The method of measuring the transmission emciency of a signalingcircuit, which consists in applying a known yamount of power to the nearend of the signaling circuit, simultaneously apply-ing power to the farend of a second circuit coterminous with theV said signaling circuit,varying the `amount Vof power applied to the said second circuit by andin accordance With the amount of power received at the distant end ofthe said signaling circuit and measuring the amount of power received atthe near end of the said second circuit.

10i The method of claim 9 further characterized by the discontinuance ofthe application of power at the near end of the signaling circuit and byIthe application of power to the far end of that circuit and themeasurement of the power received at the near end of such circuit.

1l. In a transmission measuring system, the combination with 'asignaling circuit, whose transmission efficiency is to be measured, of asecond circuit coterminous with the said signaling circuit, a source ofcurrent of iixed magnitude, a current measuring device, both located atthe near ends of said circuits, a second source of current of xedmagnitude connected to theY distant end of said second circuit, the saidconnection being shunted by Aan impedance adapted to be varied, anamplifier having a rectifier connected to the output side thereof, animpedance also connected to the output of said amplifiers, switchingmeans at the near end arranged to connect said first mentioned source tosaid signaling circuit and said measuring device to said second circuitand a second switching means at the distant end to connect that end ofsaid sig,- naling circuit to the input side of the said arn-pliiier.

i2. The arrangement of claim ll vclfiaracterized by means to control theseveral switching means whereby the source of current at the near endmay be disconnected from said signaling circuit and the said measuringdevice may be connected thereto, and simultaneously the distant terminalof said signaling circuit may be disconnected from the said amplifierand connected to the said second source of current thereby transmittingcurrent over the said signaling circuit in the direction opposite tothat in which it was transmitted theretofore.

JOSEPH?. ANDREWS.

